Recently, the VTR is becoming higher in picture quality and higher in sound quality, and the magnetic disk apparatus has come to be higher in capacity and faster in speed. Accordingly, the magnetic recording medium is demanded to be higher in recording density. As the magnetic recording medium to meet this demand, a magnetic recording medium of ferromagnetic thin film type is known, and it is intensively developed and realized. The prior arts of the magnetic recording medium of this type include the Japanese Patent Laid-Open No. 62-58416 (prior art 1), No. 1-184722 (prior art 2), No. 2-125417 (prior art 3), No. 2-126418 (prior art 4), and No. 4-134623 (prior art 5).
Prior art 1 relates to a magnetic recording medium having a protective layer of organic high molecular compound with the ratio of nitrogen (N)/carbon (C) of 40 atomic % or more, provided on a ferromagnetic thin film. Prior art 2 relates to a magnetic recording medium having a hard carbon thin film containing boron (B), titanium (Ti) or silicon (Si), provided on a ferromagnetic thin film. Prior art 3 relates to a magnetic recording medium having a hard carbon film provided on a ferromagnetic thin film, having a plasma polymerization film involving nitrogen provided on the hard carbon film, and having a lubricant layer containing fluorinated carboxylic acid provided on the polymerization film containing nitrogen. Prior art 4 relates to a magnetic recording medium having a hard carbon film provided on a ferromagnetic thin film, treating the hard carbon film surface by glow discharge in the presence of ammonia gas, and having a lubricant layer containing fluorinated carboxylic acid provided on the hard carbon film. The carbon protective film provided on the ferromagnetic thin film of prior art 5 has the relative intensity of Raman bands (1400 cm.sup.-1 band/1550 cm.sup.-1 band) of 2.6 to 3.8.
However, even in these prior arts, a further improvement was necessary in order to obtain a magnetic recording medium excellent in electromagnetic conversion characteristic, running stability, running durability, and weatherability.
For example, in the constitution of prior art 1 in which the protective layer of organic high molecular compound with the ratio of N/C of 40 atomic % or more is provided on the ferromagnetic thin film, the hardness of the protective layer of organic high molecular compound itself (film thickness:15 nm) is lowered and is easily worn, and hence running stability and running durability cannot be satisfied sufficiently. In the constitution of prior art 2 in which the lubricant layer is provided on the hard carbon thin film containing B, Ti and Si, although the adhesion strength between hard carbon thin film and lubricant layer is improved, the hardness of the hard carbon thin film itself (film thickness:8 nm) is lowered, and hence the durability of still characteristics or the like is worsened. In the constitution of prior art 3 in which the plasma polymerization film containing nitrogen (film thickness:3 nm) is provided between hard carbon film and lubricant layer, but the plasma polymerization film containing nitrogen is too thick, low in hardness and easily worn, and hence the running stability and running durability cannot be satisfied sufficiently. In the constitution of prior art 4 in which the lubricant layer is provided after treating the hard carbon film surface by glow discharge in the presence of ammonia gas, since the surface of the hard carbon film is heavily damaged by the impact of charged particles generated from ammonia, durability, and weatherability are lowered. In prior art 5, in order to obtain the optimum hardness, toughness and coefficient of kinematic friction of the carbon protective film (film thickness:15 nm), the relative intensity of Raman bands (1400 cm.sup.-1 band/1550 cm.sup.-1 band) is defined in a range of 2.6 to 3.8, but weatherability is not sufficient.